The present invention relates to a vertical takeoff and landing (VTOL) aircraft, and more particularly to a drag reduction system for an external load carried thereby.
Future military forces require enhanced vertical lift capabilities in a compact package. The CH-53E is currently the world's largest shipboard compatible helicopter. A significant consideration in the design of the CH-53E was shipboard compatibility. The CH-53E effectively defines the maximum aircraft spatial capacity, which will fit on the elevators and in the hangar deck of United States Marine Corps Amphibious Assault Ships, more commonly called an LHA or LHD. Emerging payload weight requirements are beyond the growth capabilities of the CH-53E while maintaining current shipboard compatibility requirements. Thus, a conventional helicopter like the CH-53E would be so large that it would not fit in the hangar deck or on the elevator of an LHA or LHD.
Super heavy lift (SHL) VTOL aircraft are generally defined as aircraft with twice the largest payload carried by current conventional helicopters. Future aircraft requirements are envisioned to be in the range of approximately 40,000 pounds of payload over a 600 mile range while being shipboard compatible.
VTOL aircraft are unique in their ability to carry loads externally. A dedicated external load configuration SHL VTOL aircraft has potential to meet the desired shipboard requirements. Disadvantageously, this configuration results in high aircraft drag due to the addition of the non-aerodynamic load beneath the aircraft. Vehicles, containers, fuel bladders, flat racks, and other loads can increase aircraft net drag anywhere from 50% to 100%. Furthermore many external loads cannot tolerate the air loads created at typical aircraft cruise speeds of around 150 kts. To avoid damage to windows, mirrors, doors, and numerous other features of vehicles and objects, external loads are often limited to around 100 kts. This further limits aircraft cruise speed and degrades range capability.
Fairings and other devices that are removably mounted to the external load are generally known. Disadvantages with this approach include the necessity of maintaining a relatively large inventory of fairings as each fairing is particularly tailored for a particular load. The fairings must also be attached and removed from the external load, which increases deployment times. Aerodynamic forces created by fairings may also be unfavorable to a slung load resulting in undesirable swinging. Attaching a device to a helicopter to fair around a slung load may also be impractical because the external loads are typically slung a relatively long distance from the aircraft underside.
Accordingly, it is desirable to provide an external load drag reduction system permanently installed on a VTOL aircraft, which permits higher cruise speeds, longer ranges, and reduced air loads on the external load.